Helping those less fortunate, what is our obligation?
This is something I personally struggle with a lot.

"If you're walking in expensive clothing and see a child drowning, do you jump in to save the child knowing that your clothing will be ruined?" Most people would ruin the clothing and save the child.
But this is the very situation we are in every day. If I buy anything other than the bare necessities, am I guilty because I am not spending that money on food or medicine that could save someone's life?
So to return to the initial dilemma, if you were walking and there were infinitely many children drowning and waiting for you to save them, when would you stop? Would you just keep doing it?
Am I a bad person if I prefer to go to movies and play computer games instead of using that money to help starving children?

You are a member of a flawed community. To focus blame on the individual is to ignore social and cultural context, and to expect one to be ascetic in a consumer society is wrong. You would live in relative poverty, and probably suffer as a result.

Therefore the onus is us to organise group action and cultural transformation, where we can go without some of our luxuries yet still have a worthwhile life, one which does not leave one languishing as an outsider.

This would involve valuing and creating an environment where free or inexpensive happiness can flourish, so that we can save and give, but not to our social and psychological detriment.

I find it more useful to phrase the question in more positive terms:
Would spending money on food or medicine that could save someone's life help me live a more fulfilled life? Am I missing out on this opportunity by spending money on movies and computer games instead?

My answer to the question is one of balance. I'm not prepared to eliminate entertainment in the form of movies and computer games.

They are fun and help me unwind. However, in most cases, dispensing with luxuries in favour of making a positive difference in the lives of other people definitely adds value to my life.

So to return to the initial dilemma, if you were walking and there were infinitely many children drowning and waiting for you to save them, when would you stop? Would you just keep doing it?

I would stop once it stopped adding value to my life. This happened a few years ago, prompting me to look for a more effective way to help them.

This may not answer your question, but I see the drowning child analogy as flawed.

If I am walking along the riverbank and see a drowning child, then I am the only person who can save him. Thus the obligation falls upon me. Now certainly there are people suffering or dying all over the world - but why does the obligation to help them, or any particular one of them, fall on me and not you, or someone else?